CspA, the major cold shock protein of Escherichia coli, negatively regulates its own gene expression

When the gene for CspA, the major cold shock protein of Escherichia coli, was disrupted by a novel positive/negative selection method, the deltacspA cells did not show any discernible growth defect at either 37 or 15 degrees C. By two-dimensional gel electrophoresis, total protein synthesis was analyzed after temperature downshift in the deltacspA strain. The production of the CspA homologs CspB and CspG increased, and the duration of their expression was prolonged, suggesting that both CspB and CspG compensate for the function of CspA in the absence of CspA during cold shock adaptation. Interestingly, the production of the 159-base 5'-untranslated region (5'-UTR) of cspA from the chromosomal cspA::cat gene, detected by primer extension, failed to be repressed after cold shock. When an independent system to produce CspA was added to the deltacspA strain, the 5'-UTR production for the cspA::cat gene was significantly reduced compared to that of the deltacspA strain. By examining the expression of translationally fused cspA and cspB genes to lacZ in the deltacspA strain, it was found that cspA is more strongly regulated by CspA than cspB is. We showed that the increased expression of the 5'-UTR of the cspA mRNA in the deltacspA strain occurred mainly at the level of transcription and, to a certain extent, at the level of mRNA stabilization. The mRNA stabilization in the deltacspA strain was observed for other mRNAs, supporting the notion that CspA functions as an mRNA chaperone to destabilize secondary structures in mRNAs.